Some mobile devices have features to determine a geographic location. For example, a mobile device can include a receiver for receiving signals from a global positioning system (GPS). The mobile device can determine a geographic location, including latitude and longitude, using the GPS signals. In many places, GPS signals can be non-existent, weak, or subject to interference such that it is not possible to determine a location using the GPS receiver on a mobile device. For example, a conventional mobile device often fails to determine a location based on GPS signals when the device is inside a building or tunnel.